The present invention is a boost switching power converter. More specifically, the present invention is a power converter for producing a DC voltage higher than that of the primary voltage source. The boost converter of the present invention is particularly adapted for use in high power applications.
A common primary electrical power found in aircraft is either +28 volt DC (VDC) or three phase 115 volt AC (VAC), which is rectified and filtered to approximately 270 VDC. Many types of equipment have been designed to operate from either of these power sources. The present invention may be used in applications in which +28 VDC is converted to +270 VDC.
Boost converters have been used for some time to convert a low DC voltage into a higher DC voltage. A common boost converter includes an inductor, a diode, an output capacitor, and a power switching device. These converters for producing a voltage higher than the voltage of the primary source are sometimes referred to as "step-up" converters.
A common, known boost converter, or step up voltage converter, is shown in FIG. 1. Operation of the illustrated boost converter is well understood in the art.
An input terminal 11 receives the input DC voltage (V.sub.in). An input capacitor 13 is connected between the input terminal 11 and ground. A current sense transformer 23 feeds a sample of the inductor current back into a regulator control 31. An inductor 21 having inductance L1 is connected to the input terminal 11 through the primary of the current sense transformer 23. A switch, such as a Field Effect Transistor (FET) 41, is connected between the "output" side of the inductor 21 and a second terminal, such as ground. The switching element 41 is controlled by a regulator control 31. The regulator control 31 governs the time the switch is on (conductive) or off (nonconductive). A rectifying diode 61 couples the output side of the inductor 21 to the converter output terminal 81. The converter output voltage V.sub.out is produced on the converter output terminal 81. An output filter capacitor 91 is connected between the output terminal and ground.
When the FET 41 is conductive, energy from the input terminal 11, passing through the current sense transformer 23, charges the inductor 21. When the FET 41 is not conductive, that energy is discharged through the diode 61 to charge the output capacitor 91. The regulator control 31 includes gate control circuitry and cycles the switch on and off. The regulator control governs the ratio of the time the FET is conductive (on) and nonconductive (off) so that the output voltage V.sub.out on the converter output terminal 81 remains constant. The regulator control adjusts the on/off cycle of the switch 41 by monitoring the voltage on the converter output terminal 81 through a feedback line 35.
As the regulator control 31 turns the transistor 41 off, the voltage at the drain of the FET 41 rises to the boost converter voltage V.sub.out, plus some overshoot due to unwanted parasitic elements.
The current drawn by the boost converter at particular times in its operating cycle can peak at a very high value, much higher than the DC input current or the DC output current. Even at moderate power levels, high peak currents make filtering difficult at both the input and the output.